From previous ObsParis / CDS meeting
Using Aladin prototype v10 (6/6/2017) and TOPCAT v4.4 on MacOS
- See also page: Aladin & planetary surfaces for older use cases / examples.
Standard planetary mapping in TOPCAT
Assuming longitude is E-handed (EPN-TAP convention, and IAU convention in planetocentric frames)
• Standard setup for planetary maps in TOPCAT SkyPlot:
(in Axes / Projection)
Projection = sin (i.e. sphere, for orthographic), but car (cylindrical) is also possible
Uncheck Reflect longitude axis,
View Sky System: Equatorial,
(in Axis / Grid)
Increase Grid Crowding cursor value to 30 or 60° tick
• Standard setup for planetary maps in TOPCAT PlanePlot (cylindrical):
(in Axes / Range)
Set Max X value to 360
Central meridian will be on left side
• To put the central meridian at the center:
(in Axes / Range)
Min / Max X = -180 / 180
(in Mark / Position)
X: LON > 180 ? Lon - 360 : Lon
(in Axes / Labels)
X Label = Longitude
Healpix generation from a table in TOPCAT
In TOPCAT, load a table containing a list of observations located in lon/lat
(working example is a large table of VIRTIS/Rosetta observations of 67P)
1) Standard way:
• Open Plane Plot panel, select table and Lon & Lat parameters in Position panel
• Go to Form panel, click on the big Forms button (green cross) and "Add SkyDensity" from the local menu. Uncheck the previous Mark Form
• Go back to Position panel, select Lon and Lat parameters (C1min and C2min for an EPN-TAP view)
• Back to the Form panel, select parameter to plot as Weight (will be weighted by density), select combine mode, and adjust scale. Healpix generation is performed on the fly.
• Possibly adapt color scale in the Aux Axis tab (left menu)
• In the Form panel, you can save the healpix map (cell #, plotting parameter) - saved at scale 12, apparently (FITS formatting is more efficient than VOTable, as it is compressed). You can also load an existing map from there.
• Add new synthetic column providing healpix cell number (right-click on table column header and enter new column description):
healpixNestIndex( 6, longitude, latitude )
(adapt scale to data in use, 6 provides a resolution of ~ 1° at the Equator)
• Open Skyplot panel, add New healpix layer, provide inputs
Correct Healpix Data Level in particular (TOPCAT will try to guess, but this is uncertain)
• In Skyplot / Style panel, use Degrade and Combine mode to reduce resolution on the fly.
Mars HiPS generation
• In Aladin, load file Mars_MGS_colorhillshade_mola_1024.jpg
(MOLA integrated relief map)
• Go to Image > astrometric calibration:
Coord = 0.,0.
pos x/y = 512, 256 (lon = 0°, lat = 0° at image center)
size = 21.1' (= 360. / 1024)
Symetry: No => this is mandatory to get the image in the correct orientation.
But this currently provides a W longitude frame (entering Yes results in a reverse image (seen from the inside), not in a reverse frame).
Edit > properties: ascending longitudes - does not change anything here
• Convert to HiPS :
Tool > Convert current image to a HiPS
• The hpx image should be saved on disk automatically
MOC use case
- Load Mars MOLA hpx in Aladin
- Select two large craters in Mars Craters service from VESPA client
- send as s_region from VESPA client (to Aladin) — (s_region is currently provided in this service with W longitudes, so this will project correctly)
- select them in Aladin with pointer
- Generate common MOC for these 2 craters (Coverage > Generate MOC > from objects)
- You can save it from File > Export Planes (save preferably as fits for reuse)
This is OK and very quick.
• Then: test intersections with something else.
How do we do that?